A known type of compressed air drying nozzle consists of a tubular body which has an annular slot on the inside via which compressed air is admitted. This compressed air flows along the wall of the tubular body and thereby produces a negative pressure, as a result of which ambient air is drawn in by a tube end which, together with the compressed air, passes out of the other tube end. The compressed air is admitted via a compressed-air line of the drying nozzle.
Organic solvent-containing lacquers can be forcibly dried with this drying nozzle. By using the drying nozzle, the drying time is clearly reduced, as a result of which spray booth run-through time is shortened.
A drying nozzle of this type is especially useful for drying water-dilutable lacquers which, due to the physical properties of water, dry substantially slower than solvent-containing lacquers. The drying speed of such lacquers depends very heavily on the humidity of the ambient air. The higher the humidity, the lower the drying speed. The increase in drying time has a detrimental effect on the use of water-dilutable lacquers, since spray booths, drying chambers or drying ovens are blocked for a relatively long time.
In order to reduce the drying time, it is known to blow dried air onto the coated object with the aforementioned drying nozzle. Drying nozzles of this type are attached either to the ceiling or fastened to a stand. It is also known to make them in the form of guns which can be manually operated. Guns of this type are used primarily for drying smaller surfaces.
The disadvantage of this known embodiment is the requirement for excessive capital expenditure.
In order to avoid the additional capital expenditure, it is known to dry smaller surfaces in particular with a paint spray gun, whereby a trigger guard is pulled only to the extent that only air but no coating materials flow through the spray nozzle. The air jet is greatly limited and has a high velocity of flow, as a result of which defects can occur in the lacquer film. In addition, due to the very limited air jet, the blown surface is too small in order to be able to economically dry larger surfaces.
U.S. Pat. No. 2,086,183 discloses a paint spray gun in which the nozzle head has a protective nozzle which has a rear circular-cylindrical section which expands conically in the direction of flow of the paint/air jet mixture. Three segmental air nozzles are provided about the paint/air nozzles and are set back from these in the area of the circular-cylindrical section of the protective nozzle, the air nozzles being directed toward a conically expanding neck on the nozzle head. The purpose of this arrangement is to surround the fanning paint/air jet by means of an air veil passing out of the segmental air nozzles in order to reduce a mist formation. In this case, ambient air is drawn in via the annular slot between the cylindrical section of the protective nozzle and the nozzle head, but only to a slight extent since the segmental air nozzles are arranged in the area of the circular-cylindrical section of the protective nozzle and the paint nozzle and the air nozzle in the conically expanding area of the protective nozzle. The purpose of this arrangement is to surround the fanning paint/air jet by means of an air veil passing out of the segmental air nozzles in order to obtain a sharply limited paint/air jet and thus reduce the formation of mist.